Conventionally, a radar device is developed which is mounted on a vehicle and detects an object around the vehicle. When such a radar device is mounted on the vehicle and exposed, there is a possibility that the radar device is weathered to cause malfunction. Further, when the radar device is mounted on the vehicle and exposed, the vehicle's appearance is likely to be defaced. Accordingly, when the radar device as described above is mounted on the vehicle, a cover for covering the radar device is mounted on the vehicle together with the radar device.
Patent Document 1 discloses the radar device as described above. The radar device disclosed in the Patent Document 1 has a radome portion through which electromagnetic waves transmitted from and received by a radar main body are transmitted. The radar main body is mounted inside a vehicle's bumper, and the above-described radome portion is formed as a part of the vehicle's bumper.    Patent Document 1: Japanese Laid-Open Patent Publication No. 11-231041